This application relates to a dyeing process and more particularly to after-dyeing treatment of fabric.
In conventional fabric or textile dyeing processes, dyeing is followed by a treatment regime which generally consists of one or more treatment baths, the purpose of this being the removal of excess dyestuff (which has not adhered to the fabric), the further treatment of the fabric (for example, by fixing agents for those dyes which require it, or by such materials as fabric softeners) or the removal of residual materials remaining after a treatment (for example, fixing agent or fabric softener). A conventional dyeing process without chemical treatments such as fixing and softening typically comprises the following sequential steps: dyeing in a dye bath, transfer to a first rinse bath (where the material is rinsed with water), transfer to a second rinse bath, transfer to a first soap bath (where the material is washed with soap solution), transfer to third and fourth rinse baths and a final drying step in a centrifuge. The whole procedure is conventionally carried out on a dyeing machine in which the dyeing was carried out, transfer to the centrifuge only being carried out for the particular purpose of centrifuging.
Recent developments in dyeing processes have been concerned with decreasing the liquor to goods ratio employed in the dyeing step. Generally a lower liquor to goods ratio results in a more effective dyeing. However, it has been observed that in conventional processes, even with low liquor to goods ratios, for example, a liquor to goods ratio in the range of from 20:1 to 5:1, a significant amount of the liquor is transferred from a dye bath to the next treatment step, which may be a rinse bath, a wash bath or some other treatment bath. This transfer continues in succeeding stages, the amount of liquid being transferred depending on the liquid up-take of the particular fabric (for example, knitted fabrics have a greater up-take than woven goods). Knitted cotton (cotton interlock) which typically has a liquid up-take of 250% by weight transfers up to a quarter of a dyeing liquor having a liquor to goods ratio of 10:1 to the next processing stage. An even greater transfer occurs with a smaller liquor to goods ratio.
It follows that this transfer of liquid reduces efficiency considerably. As a result, the potential effect of the particular processing stage, be it rinsing, washing, fixing, softening or other effect, of the bath is decreased. Thus, more washing procedures are required in order to arrive at a fabric having the desired level of freedom from undesirable materials such as excess dyestuff or other impurities (such as process chemicals). The increase in number of washing procedures required, means an increase in one or more of the overall water consumption, overall time requirement and overall energy consumption for the process. This in turn increases the cost of production and the cost to the consumer. So far, it has not proved possible to improve the conventional methods to any great extent.
The present invention provides a dyeing process, which comprises the steps of applying a dyeing liquor to a fabric to be dyed, and thereafter subjecting the fabric to a treatment regime, which comprises a series of liquid bath treatment steps, characterized in that the fabric is subjected to centrifugation after each such treatment step.